What does :%S do in vim?

As I tried to globally repla开发者_C百科ce FOO with BAR in a vim buffer, I accidentally typed

:%S/FOO/BAR/

Note the uppercase S instead of the more suitable s.

Of course, it wouldn't replace my FOOs. That's understandable. Yet, vim split the window into two windows, both holding the same buffer.

Unfortunately, I was unable to find any :help on this behaviour. So, can someone explain what the uppercase :%S is supposed to do and where I can find help on it?

:h :S

:[N]Sexplore[!] [dir]... Split&Explore current file's directory *:Sexplore*